1. Field of the Invention
The present invention relates to a heat treating apparatus and method for heat treating substrates such as semiconductor wafers by irradiating the substrates with light.
2. Description of the Related Art
A heat treating apparatus such as a lamp annealing apparatus with halogen lamps is used to execute a step of activating ions implanted in a semiconductor wafer. Such a heat treating apparatus activates ions in the semiconductor wafer by heating the wafer to a temperature of about 1,000 to 1,100 deg C., for example. Then, the heat treating apparatus heats the wafer at a rate of some several hundred degrees per second by using the energy of light emitted from the halogen lamps.
However, it has been found that, even when ions in the semiconductor wafer are activated by using the heat treating apparatus that heats the wafer at the rate of several hundred degrees per second, the ions implanted in the semiconductor wafer present a blunt profile, that is the ions become dispersed. When such a phenomenon occurs, the ions become dispersed even though implanted in high concentration into the surface of the semiconductor wafer, and hence a problem of having to implant the ions in a larger amount than is necessary.
To solve the above problem, it is conceivable to use xenon flashlamps, for example, to irradiate the surface of the semiconductor wafer with flashes, thereby to heat, within an extremely short time, only the surface of the semiconductor wafer implanted with ions. However, although the surface of the semiconductor wafer may be heated very quickly by using xenon flashlamps, the wafer is heated only to 500 degrees or thereabouts. It is impossible to heat the semiconductor wafer to the temperature of about 1,000 to 1,100 deg C. necessary for activating the ions in the wafer.
On the other hand, Japanese Patent Publication (Unexamined) No. 2001-237195, by way of addressing the above problem, discloses a heat treating apparatus having a preheating device for preheating a substrate before heating the substrate by xenon flashlamps.
With such a heat treating apparatus, flashes from the xenon flashlamps may cause a reaction of the gas in the heat treating chamber storing the semiconductor wafer. Where, for example, oxygen is present in the gas, ozone is momentarily generated from the oxygen to lower the pressure in the heat treating chamber in an instant. Such a sudden pressure drop produces a relatively loud sound, i.e. vibration. This vibration scatters particles in the heat treating chamber, and hence a problem of the particles adhering to the semiconductor wafer under heat treatment. In an extreme case, the vibration could move the semiconductor wafer.
The gas in the heat treating chamber circulates therein by convection. It is therefore difficult to heat the surface of the semiconductor wafer uniformly in time of preheating by the preheating device or flash heating by the xenon flashlamps.
Further, the above heat treating apparatus has numerous materials for sealing the heat treating chamber or maintaining the chamber at a high temperature. Where oxygen is present in the heat treating chamber, these materials are oxidized in time of flash heating by the xenon flashlamps, thereby shortening the service life of the heat treating chamber. Where the gas in the heat treating chamber contains organic substances, these substances become melanized and adhere to a translucent plate forming the heat treating chamber, to reduce the life of the heat treating chamber.